The Assume model is linear checkbox on the Model Generator tab:

can be used for minimizing memory usage on models that are entirely linear.  When this option is in effect, the model generator can take steps to dramatically reduce overall memory consumption without sacrificing performance.  In fact, if all your models are linear, we recommend that you enable this option permanently as the default for your installation.  The one restriction is that the model must prove to be entirely linear.  If a single nonlinearity is detected, you will receive an error message stating that the model is nonlinear and model generation will cease.  At which point, you should clear this option and attempt to solve the model again.

By default, the Assume model is linear option is disabled.